Method of forming colored copied image

ABSTRACT

Method for obtaining a colored copied image by repeating a cycle consisting of the process of forming an electrostatic latent image on an electrophotographic copying material having a photoconductive layer, the process of transferring said electrostatic latent image onto a transfer sheet having a dielectric layer and the process of developing the thus transferred electrostatic latent image for each primary color of the colored original image, an improved method of forming a colored copied image free of fog which method comprises employing a transfer sheet having a dielectric layer containing a photoconductive substance and interposing an additional process of applying active radiant rays to the whole surface of said dielectric layer upon which the image is developed between said cycles, and a transfer sheet useful in the method.

United States Patent [1 1 Arai [ Mar. 18, 1975 [75] Inventor: Akio Arai, Tokyo, Japan [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo,

Japan [22] Filed: Dec. 28, 1973 [21] Appl. N0.: 429,146

[301 Foreign Application Priority Data Jan. 19, l973 Japan 48-7889 [52] US. Cl 96/1.2, 96/1 R, ll7/l7.5 [5|] Int. Cl G03g 13/22 [58] Field of Search 96/1 TE, 1 R, 1.2, 1.4; ll7/17.5

[56] References Cited UNITED STATES PATENTS 1666.458 5/1972 Arneth et al 96/1 TE Primary Examiner-Norman G. Torchin Assistant Examiner-L. Falasco Attorney, Agent, or FirmCooper, Dunham, Clark, Griffin & Moran 57 ABSTRACT Method for obtaining a colored copied image by repeating a cycle consisting of the process of forming an electrostatic latent image on an electrophotographic copying material having a photoconductive layer, the process of transferring said electrostatic latent image onto a transfer sheet having a dielectric layer and the process of developing the thus transferred electrostatic latent image for each primary color of the colored original image, an improved method of forming a colored copied image free of fog which method comprises employing a transfer sheet having a dielectric layer containing a photoconductive substance and interposing an additional process of applying active radiant rays to the whole surface of said dielectric layer upon which the image is developed between said cycles, and a transfer sheet useful in the method.

10 Claims, N0 Drawings METHOD OF FORMING COLORED COPIED IMAGE BACKGROUND OF THE INVENTION a. Field of the Invention The present invention relates to improved methods for forming a colored copied image through the process of transferring an electrostatic latent image.

b. Description of the Prior Art As one of the methods for forming a colored copied image by the use of electrophotographic copying material consisting of a photoconductive layer and a support, there is known an image-transferring method employing a transfer sheet in which there is a repeating cycle consisting of electrification of the copying material, exposure of the colored original image upon color separation thereof into three primary colors, development with a yellow-color toner developer, a magentacolor toner developer and a cyan-color toner developer successively to form a copied image and finally transferring the thus formed copied image onto a transfer sheet such as an ordinary paper. There is also known an electrostatic transferring method for forming a colored copied image on a transfer sheet consisting of a support and a dielectric layer of insulating resin by repeating a cycle consisting of forming an electrostatic latent image on a copying material through electrification of said copying material and exposure of a colored original image upon color separation thereof into three primary colors, transferring the thus formed electrostatic latent image onto a transfer sheet having a dielectric layer of insulating resin and developing the transferred latent image. The former method is defective in that, in that it is necessary to form a temporary toner image on an electrophotographic copying paper and then transfer the image onto a transfer sheet, the electrophotographic copying material may be damaged. The latter method has the merit that, since an electrostatic latent image formed on an electrophotographic copying material is transferred onto a transfer sheet electrically without developing the latent image, the copying material is less likely to become damaged. However, according to the latter method, some of the electric charge from the electrostatic latent image transferred onto the transfer sheet remains even after development, This causes the developer to attach to the part having the residual electric charge during the second cycle and the following cycles, giving rise to the phenomenon called fog which makes the reproduction of faithful colored images difficult.

SUMMARY OF THE INVENTION The present invention provides methods of producing colored copied images through the electrostatic latent image transferring process, in which there is rapid extinction of the residual electric charge and the production of colored images free of fog.

More precisely, the present invention provides methods of forming colored copied images characterized in that, the transfer sheet contains a photoconductive substance in the dielectric layer thereof and that there is an additional process step of applying active radiant rays to the whole surface of said dielectric layer which is interposed between the cycles.

The transfer sheet for use in the present invention is composed by providing a dielectric layer containing an inorganic or organic photoconductive substance on a used. These include, for example, acrylic resins, vinyl chloride vinyl acetate copolymers, butadiene styrene copolymers, alkyl-(metha)acrylate styrene copolymers, alkyl(metha)acrylate butadiene copolymers, silicone resins, alkyd resins and the like.

Suitable inorganic photoconductive pigments for use in this invention include white-colored or light-colored zinc oxide, titanium oxide, etc.

Suitable organic photoconductive pigments for use in this invention include colorless or light-colored pigments such as anthracene, oxadiazole, thiadiazole, aminothiazole, triazole, oxazole, thiazole, quinazoline, acridine and the like. Sensitizers which may be employed include, any of the sensitizers conventionally employed in the field, but it is essential that these sensitizers possess spectrosensitivity in each sphere of blue, green and red, that is 400-500 um, 500-600 mp. and 600-700 ma. To cite suitable sensitizers, there are Crystal Violet, Malachite Green, Methyl Violet, Acridine Yellow, Bromophenol Blue, Erythrosine, Rose Bengale, Thymol Blue and 2,4,7-trinitrofluorenone. These sensitizers are utilized in amounts of 5X10 mole to 5X10 mole for each g of photoconductive substance employed.

In the transfer sheet for use in electrostatic transferring of the present invention, in the case of employing an inorganic or organic photoconductive pigment for the dielectric layer thereof, it is essential to select an appropriate mixing ratio of the insulating resin and the photoconductive pigment, and it is appropriate to mix the photoconductive pigment at a rate of0.35 parts by weight and preferably 0.5 2.5 parts by weight for each part by weight of the insulating resin. In the case where the amount of the photoconductive pigment is less than 0.3 part by weight, there is not a sufficient extinction of the residual electric charge even when the whole surface of the dielectric layer is exposed to light, while in the case where said amount is in excess of 5 parts by weight, the surface texture of the dielectric layer becomes coarse, causing not only the lowering of the transfer efficiency of electrostatic charge [l-(surface potential on copying material after transferring)/(surface potential on copying material before transferring)] but also the loss of the paperlike feeling when the support is paper, so that both cases are undesirable.

For the purpose of improving the surface properties, such as writability, of the dielectric layer, such modifying agents as starch, silica, polyethylene particles and the like may be added.

In the present invention, in the case where an organic photoconductive resin (which is concurrently an insulating resin) is employed for the dielectric layer, it is necessary to employ an inorganic white pigment such as silica, zinc oxide, titanium oxide, etc. together with it, and, as in the case of the aforesaid insulating resin photoconductive pigment-containing dielectric layer, addition of a sensitizer is preferable.

Inasmuch as organic photoconductive resins have insulating properties, it is not necessary to employ additional insulating resins with them. Typically useful organic photoconductive resins include for instance, poly-N-vinylcarbazole or its halogenated derivatives, polyvinylanthracene or its derivatives and the like.

In the case of employing an organic photoconductive resin, the appropriate weight ratio of the inorganic white pigment to the organic photoconductive resin is in the range of 0. l5 and preferably 0.3-3. In the case where this weight ratio is less than 0.1, the paperlike feeling is lost, while if it is in excess of 5, the transfer efficiency is lowered. Both cases are undesirable.

The thickness of the dielectric layer in the present invention can be varied within the range of l30 ,u, and a satisfactory thicknessis in therange of 5-15 t.

There follows a description of how to form a colored copied image according to the present invention.

An electrophotographic copying material prepared by providing a photoconductive layer on a support is charged with electricity by corona discharge, and then an electrostatic latent image is formed on said copying material by applying white light from tungsten lamp reflected from or passed through a colored original image through a red filter (color separation of the colored original image is effected through this process). Next, by superposing a transfer sheet of this invention on this electrostatic latent image, the electrostatic latent image is transferred onto the dielectric layer of the transfer sheet, and then the electrostatic latent image thus transferred onto the dielectric layer is developed with a developer containing cyan-color toner particles and fixed. Upon completion of the cycle of the foregoing processes, by applying, for instance, active radiant rays having a luminous intensity ranging from several hundreds to several thousands luxes to the whole surface of the dielectric layer for 1 second, the residual electric charge on the dielectric layer is extinguished. Subsequently, by repeating the same cycle as above except for replacing the red filter used therein with a green filter and a blue filter in succession and the developer containing cyan-color toner particles with a developer containing magenta-color toner particles and a devel oper containing yellow-color toner particles in succession and the same overall application of radiant rays as above, a colored copied image corresponding to the colored orginal can be formed on the transfer sheet. If desired for the formation of a copied image according to this invention, it is possible to add another cycle comprising application of a developer containing black-color toner particles the foregoing processes for the purpose of adjusting the brightness. The overall application of radiant rays is no longer needed after the final cycle. It should be noted that the order of color separation is not limited to the order described above.

Any of the conventional developers for cyan, magenta and yellow colors may be used in this invention. Particulars of such developers have been disclosed in, for instance, U.S. Pat. No. 3,010,842 and US. Pat. No. 3,140,175.

It is to be noted that the above described electrophotographic copying material and the process of forming an electrostatic latent image thereon is just one embodiment of the present invention. The invention is also applicable to other electrophotographic processes known heretofore which employ electrophotographic DESCRlPTlON OF THE PREFERRED EMBODIMENTS EXAMPLE 1 Composition of dielectric layer forming liquid:

50% toluene solution of vinyl toluene-butadiene copolymer (molar ratio 50:50)

zinc oxide (mean particle diameter: 0.5 t)

0.5% methanol solution of fluoresceine 01% methanol solution of Methylene Blue 1.0% methanol solution of Rose Bengale toluene parts by weight 5 parts by weight 0.5 part by weight 1.0 part by weight 1.0 part by weight 200 parts by weight A mixture having the above composition was dispersed for 20 minutes by means of a homomixer. The

resulting dispersion was coated on a paper support treated for imparting conductivity by the use of a wire bar to the extent of about 10 p. in dry thickness, and dried thereafter, whereby a transfer sheet was prepared.

The surface of an electrophotographic copying material prepared by depositing selenium on an aluminum sheet through vacuum evaporation was impressed with positive electricity (surface potential: +800V) by corona discharge. Next, white light of a tungsten lamp was applied onto a colored original image and the rays reflected therefrom were applied to the copying material through a red filter, whereby an electrostatic latent image was formed. Then, after electrically connecting the support of the transfer sheet with the support of the copying material by superposing the dielectric layer of the transfer sheet on said electrostatic latent image, the transfer sheet was stripped off.

Subsequently, the electrostatic latent image transferred onto the transfer sheet was subjected to cascadesystem development by the use of an electrophotographic dry developer consisting of a mixture of cyancolor toner particles and glass particles having a mean particle diameter of 10 t, followed by thermal fixing. Thereafter, by exposing the whole surface of the transfer sheet to white light of a tungsten lamp having a luminous intensity of 5,000 luxes/sec., the residual electric charge was extinguished.

Next, an electrostatic latent image formed by impressing electricity on the foregoing electrophotographic copying material and exposing it to rays reflected from the colored original image through a blue filter was transferred onto the dielectric layer of the foregoing transfer sheet to see that the positions of images agree with each other, developed with a developer consisting of yellow-color toner particles and glass particles and subjected to thermal fixing. Thereafter, by exposing the whole surface of the transfer sheet to white light of a tungsten lamp having a luminous intensity of 5,000 luxes/sec, the residual electric charge was extinguished.

polybutyl methacrylate polystyrene blue-sky base 25 parts by weight 65 parts by weight parts by weight EXAMPLE 2 Composition of dielectric layer forming liquid:

It); chlorobcnzcnc solution of polyvinyl carbazolc llllt. oxide chlorobenzcne 500 parts by weight 10 parts by weight 300 parts by weight A mixture having the above composition was dispersed for 20 minutes by means of a homomixer. The resulting dispersion was coated on a paper treated for imparting conductivity to the extent of about 8 p. in dry thickness, whereby a transfer sheet was prepared.

Preparation of electrophotographic copying material:

lO chlorobenzene solution of polyvinyl carbazole trinitrofluorenone chlorobenzene 200 parts by weight 20 parts by weight l5O parts by weight A mixture liquid having the above composition was coated to the extent of about 13 [J- in dry thickness on a polyethylene film having aluminum deposited thereon through vacuum evaporation, and dried, whereby an electrophotographic copying material was prepared.

By charging the thus prepared electrophotographic copying material with electricity (surface potential: 620V) by corona discharge and effecting exposure by applying tungsten lamp light reflected from a colored original image through a red filter, an electrostatic latent image was formed. Subsequently, the aforesaid transfer sheet was laid on this electrophotographic copying material so as to bring the dielectric layer of the former into contact with the electrostatic latent image on the latter, DC voltage of 1 KV was impressed between two electrodes, namely, aluminum conductive layer of the electrophotographic copying material as the cathode and the conductive support of the transfer sheet as the anode, for about 1 second and thereafter the transfer sheet was stripped off, whereby a latent image was transferred onto the dielectric layer. This latent image was then developed with a cyan-color liquid developer and further a white light having a luminous intensity of5,000 luxes/sec. was applied onto the whole surface of the dielectric layer.

By repeating the same process three times except for the modifications that the red filter was replaced with a blue filter or a green filter or no filter was used, and the cyan-color liquid developer was replaced with a yellow-color liquid developer, a magenta-color liquid developer and a black-color liquid developer, respectively, a colored copied image was formed on the dielectric layer. This colored copied image was reasonably faithful to the original image.

The developers employed in the present example were prepared through the following procedures:

Composition of cyan-color liquid developer:

Victoria Blue 25 g Beckozol I352 solution (isophthalic acid long-oil alkyd resin; solid content the manufacture of Reichhold Co.) I00 g By dispersing a kneaded mixture having the above composition in l l of Isopar H (the manufacture of ESSO Chemicals, Inc.), a cyan-color liquid developer was prepared.

Next, in the same way as above except for replacing Victoria Blue with Spilon Yellow, Brilliant Carmine 6B and Spilon Black, respectively, a yellow-color, magenta-color and black-color liquid developers were prepared.

What is claimed is:

1. In a method of forming a colored copied image on a transfer sheet by repeating a cycle comprising (1) forming an electrostatic latent image on an electrophotographic copying material having a photoconductive layer, (2) transferring said electrostatic latent image onto a transfer sheet having a dielectric layer which is an insulating resin and (3) developing the thus transferred electrostatic latent image for each primary color constituting the colored original image; the improvement comprising employing a transfer sheet having a photoconductive dielectric layer upon which the image is developed and applying active radiant rays to the whole surface of said dielectric layer between successive cycles to dissipate residual charge from a previous cycle.

2. A method according to claim 1, wherein said dielectric layer comprises an inorganic photoconductive pigment in an insulating resin.

3. A method according to claim 2, wherein the amount of said inorganic photoconductive pigment is in the range of 0.3-5 parts by weight relative to 1 part by weight of said insulating resin.

4. A method according to claim 1, wherein said dielectric layer comprises an organic photoconductive pigment in an insulating resin.

5. A method according to claim 4, wherein the amount of said organic photoconductive pigment is in the range of 0.3-5 parts by weight relative to 1 part by weight of said insulating resin.

6. A method according to claim 1, wherein said dielectric layer of the transfer sheet is an organic photo- 9. A method according to claim 8, wherein the amount of said sensitizer is in the range of 5 X 10" mol to 5 X 10* mol relative to the amount of g of said photoconductive substance.

10. A method according to claim 1, wherein said active radiant rays are applied until the residual electric charge on the dielectric layer is extinguished.

* l l l 

1. IN A METHOD OF FORMING A COLORED COPIED IMAGE ON A TRANSFER SHEET BY REPEATING A CYCLE COMPRISING (1) FORMING AN ELECTROSTATIC LATENT IMAGE ON AN ELECTROPHOTOGRAPHIC COPYING MATERIAL HAVING A PHOTOCONDUCTIVE LAYER, (2) TRANSFERRING SAID ELECTROSTATIC LATENT IMAGE ONTO A TRANSFER SHEET HAVING A DIELECTRIC LAYER WHICH IS AN INSULATING RESIN AND (3) DEVELOPING THE THUS TRANSFERRED ELECTROSTATIC LATENT IMAGE FOR EACH PRIMARY COLOR CONSTITUTING THE COLORED ORIGINAL IMAGE; THE IMPROVEMENT COMPRISING EMPLOYING A TRANSFER SHEET HAVING A PHOTOCONDUCTIVE DIELECTRIC LAYER UPON WHICH THE IMAGE IS DEVELOPED AND APPLYING ACTIVE RADIANT RAYS TO THE WHOLE SURFACE OF SAID DIELECTRIC LAYER BETWEEN SUCCESSIVE CYCLES TO DISSIPATE RESIDUAL CHARGE FROM A PREVIOUS CYCLE.
 2. A method according to claim 1, wherein said dielectric layer comprises an inorganic photoconductive pigment in an insulating resin.
 3. A method according to claim 2, wherein the amount of said inorganic photoconductive pigment is in the range of 0.3-5 parts by weight relative to 1 part by weight of said insulating resin.
 4. A method according to claim 1, wherein said dielectric layer comprises an organic photoconductive pigment in an insulating resin.
 5. A method according to claim 4, wherein the amount of said organic photoconductive pigment is in the range of 0.3-5 parts by weight relative to 1 part by weight of said insulating resin.
 6. A method according to claim 1, wherein said dielectric layer of the transfer sheet is an organic photoconductive insulating resin and said dielectric layer further contains an inorganic white pigment.
 7. A method according to claim 6, wherein the ratio of said inorganic white pigment to said organic photoconductive insulating resin by weight is in the range of 0.1-5.
 8. A method according to claim 1, wherein said dielectric layer further contains a sensitizer.
 9. A method according to claim 8, wherein the amount of said sensitizer is in the range of 5 X 10 6 mol to 5 X 10 4 mol relative to the amount of 100 g of said photoconductive substance.
 10. A method according to claim 1, wherein said active radiant rays are applied until the residual electric charge on the dielectric layer is extinguished. 